We have thousands of xml in Docbook and uses custom DTD files as shown below.
The second line in my docbook xml is as shown below
I am using Oxygen XML developer to convert these topics to DITA.
How to configure Oxygen XML to transform these custom docbook topics to DITA? Please help me with detailed steps.

if you open a standard Docbook file in Oxygen (for example the one in "OXYGEN_INSTALL_DIR\samples\docbook\v5\sample.xml" and click the "Configure Transformation Scenarios" dialog, there is a predefined transformation scenario there called DocBook to DITA. Maybe you can duplicate that transformation scenario and then use it also for your Docbook-like XML documents.
If you want to batch apply a transformation scenario, you can right click a folder containing the XML files in the Oxygen Project view and then choose "Transform with" and choose the transformation scenario to use.

I tried those steps, the output Dita files doesn't have any contents.
Hope I explained my problem in a way that was understandable by you.
How to convert a custom docbook xml which is based on a custom dtd file into DITA?